Cable railways are being used more and more frequently, especially in cities, as a substitute for over- or underground metropolitan railways. They offer the advantage that they can be integrated into the town relatively independently of topography and existing buildings and infrastructure, and so can transport people and goods quickly as an independent traffic system. They connect two or more points over the respectively shortest possible route—the air line. Such cable railways are normally linked into the public transport networks and operate without interruption for up to 20 hours a day. The resulting high stress to which the cable and components of the cable railway system are subjected due to the large number of cable revolutions causes comparably accelerated material fatigue and increased wear, and so in urban systems, in contrast to, for example, mountain railways, the criteria for discarding cables are met considerably earlier, often after just a few years of operation.
However, operating failures are very undesirable and, in addition, are expensive, especially as in urban systems they generally result in an interruption of the public transport system. Work on the cable, for example cable shortening, splice renovation, repair work or also the replacement of a cable, is time-consuming and so must be planned in good time in order to minimize disruption to the regular cable railway operation. In addition, there is often the problem that when fitting a new cable there is too little free space for the joining of a revolving cable by splicing, and in towns this can even lead to roads or squares having to be blocked in order to be able to carry out the splicing work.
In order to recognize the discard state or the end of the life span of a cable, standardized discard criteria are applied. These standards, which are often country-specific, also prescribe the inspection intervals within which the cable must be inspected by an authorized test center, e.g., by means of magnetic test methods. Depending on the state of the cable and the anticipated number of bending cycles within a specific period of time, the inspection interval is reduced by the expert, and it is thus ensured that a follow-up inspection will be carried out before a critical state occurs.
For conventional mountain railways with a relatively short daily operating period and/or seasonally limited operation and so an accordingly small number of bending cycles per year, the inspection interval can be extended to a maximum if the cable is in a good state. Running cables (revolving cables or cables in reversing operation) of such systems can achieve life spans in the order of over 20 years depending on the operating conditions.
In urban cable railway systems, the inspection interval must be considerably reduced on the basis of the much longer daily operating period and operation throughout the year and the resulting large number of bending cycles. The period of use of a running cable in an urban system, i.e., the time until the discard state has been reached, can even be shorter than the maximum inspection interval. The inspection cycles must also be set to less than a year, depending on the state of the cable, in order to ensure that the discard state can be recognized.
In addition to the inspection of the cable by an expert, visual inspections are prescribed that must be carried out by the operator itself. This type of visual check is carried out with the human eye or can be backed up by technical systems.